Bomb Squad

The Bomb Squad Achievement / Trophy can be aquired after you free Batman from the trap near the end of the Harley Quinn DLC. After he is freed he says that he will begin defusing the bombs located throughout the level. The timer will not start until after you diffuse the first bomb and a short piece of commentary plays.

Exit Theatre Mode

As soon as you diffuse the first bomb, move to the large doorway on the far side of the room. Once it opens the timer will begin. In the next room you'll encounter some thugs that you'll need to take out as fast as you possibly can.

A simple way to attain this trophy is to die or fail right before the last one is diffused, when you revive you are given ample time to finish it within the 3 minutes.